Tetanus, Biology

Tetanus

This is an infectious, non-febrile disease of animals and man, and is characterised by spasmodic tetany and hyperaesthesia. The causative agent is Clostridium tetani, a rod-shaped anaerobe with rounded ends. It forms a terminal spore, which is twice the width of micro-organism and gives an appearance similar to drumstick. The spores are highly resistant and withstand desiccation indefinitely and 5% phenol for 15 hours. The micro-organism produces a highly potent toxin which results in disease and death.

Transmission: Infection takes place by contamination of wounds. Deep punctured wounds provide favourable conditions for the spores to germinate, multiply and produce toxin which is subsequently absorbed in the animal body. The micro-organism is present in soil and in animal faeces, and is carried into the wound by a penetrating object. The organism is present in the intestine of normal animals, and under some undetermined conditions multiplies rapidly and produces toxin in sufficient quantities to be absorbed and cause the disease.

Symptoms: The incubation period is generally 1-2 weeks but it may be as short as 3 days. Tetanus affects many species of domesticated animals but occurs particularly in horses and lambs, less frequently in adult sheep, goats, cattle, pigs, dogs and cats, and rarely in poultry. Sometimes the disease develops after a history of wound, surgical interference, shearing, docking or even injection. The initial symptoms are mild stiffness and an unwillingness to move in all the animals. More severe symptoms develop after 12-24 hours which are stiffness of limbs, neck, head, tail and twitching of muscles.The spasms develop in response to noise. In terminal stages ears are erect, nostrils dilated, nictitating membrane protruded. Mastication becomes very difficult because mouth cannot be opened, hence the name lockjaw. Human beings are also highly susceptible.

Lesions: There are no characteristic lesions but sometimes aspiration pneumonia is seen in a few animals.

Diagnosis: The diagnosis is usually reached from the characteristic symptoms and isolation of organism from the wounds. No characteristic lesions develop which can be observed on post-mortem examination.

Treatment: In cattle the chances of recovery with treatment are better than in horses or sheep. The treatment is carried out by first injecting antitoxin [1 million international unit (I.U.) for a horse] then treating the wound. Penicillin given parenterally is beneficial. Muscular relaxation is achieved by injection of relaxants. The animal should be kept in a dark room and fed with the help of stomach tube.

Control: Proper hygiene and cleanliness at castration and other surgical procedures should be observed. Active immunization of horses with alum-precipitated toxoid has proved to be of value. Usually 2-3 injections are to be given. Annual vaccination thereafter is valuable in enzootic areas. Sheep should be given two injections three weeks apart to develop a solid immunity.